Method and apparatus for preparing very soluble fine powders from liquids



Nov. 26, 1963 c. ANDERMATT METHOD AND APPARATUS FOR PREPARING VERYSOLUBLE FINE POWDERS FROM LIQUIDS Filed April 26, 1960 INVENTOR CARLANDERMATT ATTORNEY United States Patent 3,112,239 METHOD AND APPARATUSFGR PREPARHNG VERY SOLUBLE FINE PDWDERS FROM LlQUlDS (Carl Anderrnatt,Ruschlihon, Zurich, Switzerland, assignor to Societe Alia-Laval, Paris,France Filed Apr. 26, 1960, Ser. No. 24,821 Qlaims priority, applicationSwitzerland May 2., 1959 3 tllairns. (til. lSfii) It is know that when aliquid containing solid substances in suspension or dissolved therein isprojected at high speed by the action of centrifugal force in the upperportion of a drying tower, a thin horizontal sheet is formed and that ifa gaseous stream of suflicient temperature is then caused to flowthrough this sheet, an instantaneous evaporation of the liquid isefifected, and that the powder subsequently collected consists ofrelatively coarse particles that are partly moderately sintered to oneanother.

The powder obtained with this known method consists of considerablecoarser particles and dissolves much better in the liquid than thatobtained through the method wherein the liquid is projected in jet formfrom fixed nozzles at a more or less high pressure.

These known advantages are reinforced and improved in installations ofthe types known and developed in the last twenty years or so, whereinthe speed of the centrifugal atomizer is adjustable continuously, andexperience teaches that the size of the grain thus obtained increased asthe speed of the centrifugal atomizer decreased.

Now it has been found, according to the present invention, that it ispossible to further increase the rate of dissolution of this powder byextracting the finest particles from the aforesaid tower and projectingthem again into said tower at very high speed, with the assistance ofcentrifugal force, in the form of a substantially horizontal sheetlocated at a level slightly above that of the liquid sheet, and to stirthese two sheets by means of drying gas fed from the tower top.

The finest particles are collected in the lower halfportion of the towerby means of a duct connected thereto, these particles being submitted tothe action of a cyclone extractor separating from the outflowing gasstream the fine solid particles, and reintroduced with one portion ofthis gas without introducing ambient air from the top of the tower andon said centrifugal atomizer.

To this end, the centrifugal atomizer comprises two superposed discs,the upper disc acting as a fan on which the fine re-cycled powder ispoured, whereas the lower one is used for atomizing the liquid.

The installation for carrying out this method comprises an atomizingdrying tower incorporating a device for separating the coarse-grainedpowder from the fine powder, a duct connecting the zone where thecoarsegraincd powder is separated from the fine powder to the top of thetower, a cyclone extractor for separating the outcoming gas from thefine powder and a fan mounted with said cyclone extractor in this duct,and a centrifugal atomizer having two discs lying in two spacedhorizontal planes mounted in the upper portion of the tower below theinlet end of said duct.

With the foregoing and other objects in view, the in vention resides inthe novel arrangement and combination of parts and in the details ofconstruction hereinafter described and claimed, it being understood thatchanges in the precise embodiment of the invention herein disclosed maybe made within the scope of what is claimed without departing from thespirit of the invention.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the accompanying drawing wherein:

FIGURE 1 is a diagrammatical axial section of the apparatus.

FIGURE 2 is another axial section showing on a larger scale details ofthe upper portion of the tower.

FIGURE 3 shows on a still larger scale and also in axial section therotary centrifugal two-stage disc; and

FIGURES 4 and 5 are horizontal sections taken along the lines lVlV andVV of FIG. 3 respectively.

The tower l illustrated in the drawing comprises a funnel-shaped orconical lower portion 2 provided with a discharge duct 3 through whichthe coarse-grained product is evacuated.

Mounted in the upper portion of the tower is a motor 4 coaxial with thetower and adapted to drive the centrifugal atomizer 5 at a relativelyhigh speed, said centrifugal atomizer having two discs lying in twospaced horizontal planes.

The liquid is fed through a pipe 6 to the annular cavity 7 merging intoa lower annular space 8 of the lower disc of the centrifugal atomizer 5,the lateral wall of this disc being perforated and provided with anumber of radial nozzles 9.

A duct it) draws from the lower portion of the tower the finestparticles by means of an exhauster or suction fan 12; in the cyclone 11these particles are separated from the outflowiug gas stream andsubsequently recycled by the fan 22 together with a moderate quantity ofgas through the pipe 13 leading to the annular hopper id from which theyflow on the disc of the upper plane 15 of the centrifugal atomizer 5;means for introducing steam or mist are provided in the form of a nozzle23 mounted in the pipe 13. This disc of the upper plane is provided witha number of orifices 16 inclined to the radius; by virtue of thisinclination this upper disc acts as a fan impeller for drawing theparticles from the discharge hopper 14 and projecting them in the formof a horizontal sheet into t-e tower.

A heated gas stream, for example at a temperature of from 150 to 180 C.,is fed through the duct 17 surrounding with its lower frusto-conical boxportion the atomizer 5 so that, in the vicinity of this disc, the sheetof fine particles is stirred together with the liquid sheet; in order tofacilitate and extend the contact between the particles of these twosheets the stream of hot gas is preferably inclined by means of battleplates 13; preferably, jackets l9 and 2t in which a cooling fluid iscirculated are provided to prevent any abnormal or overheating of theupper central zone of the tower wherein the atmosphere is constantlykept for example at a temperature of from to C.

In the absence of an atomizer having two discs it was hitherto observedthat in certain cases the hot gas flowing directly against the atomizerhaving a single disc was a cause of local overheating of the discmaterial, this entailing coagulations at the contact and deposits withcertain liquids, so that more frequent cleaning operations are requiredfor the machine.

According to this invention, there is collected through the sole outletorifice 3 of the tower it a powder of which the overheating has thusbeen avoided, its density and moisture content being substantially thesame as those obtained without the aforesaid re-cycling, but this powderdisplays the property of dissolving much more rapidly in the liquidbecause the fine powder particles have more or less sintered orexpanded.

This method is applicable to the preparation not only of powders of anydescription but also of a milky powder as well as powders obtained bymixing milk with other products.

Of course, various changes and variations may be brought to the presentinvention without departing from the spirit and scope thereof as setforth in the appended claims.

What I claim is:

l. A method of treating a liquid mixture containing solid matterdissolved or suspended therein in order to recover the solid matter individed form, very soluble in a liquid, consisting in projecting thisliquid mixture at very high speed with the assistance of centrifugalforce and in the form of a thin horizontal sheet in the upper portion ofa hot-atmosphere drying tower, and to collect the powdered product atthe bottom of said tower, according to which the finest particles of thepowdered product are extracted by suction in said tower below thehorizontal sheet of liquid mixture and are projected at very high speedwith the assistance of centrifugal force and in the form of a thinhorizontal sheet at a level higher than that of said sheet of liquidmixture and a gas is blown through these sheets in order to blow thesheet of the finest particles of the powdered product against the sheetof liquid mixture.

2. A method as set forth in claim 1, in which the main gas is blown inan inclined direction from top to bottom and from the periphery towardthe axis.

3. An apparatus for preparing a powder very soluble in liquids from aliquid containing solid substances suspended or dissolved therein, whichcomprises a tower,

a centrifugal atomizer having two discs lying in two spaced horizontalplanes in the upper portion of said tower, means for rotatably drivingsaid centrifugal atomizer at a relatively high speed, an inlet for theliquid and a duct for delivering same to the disc of the lower plane ofthe centrifugal atomizer, means for blowing a hot gas into said tower ina downward inclined direction, and above said centrifugal atomizer, adischarge orifice at the lower portion of said tower for discharging thesoluble powdered finished product thus produced, and means forwithdrawing from the central part of the tower the finest particles thusproduced and delivering them to the disc of the upper plane of saidatomizer.

References Cited in the file of this patent UNITED STATES PATENTS1,157,935 Gray Oct. 26, 1915 1,823,844 Riley Sept. 15, 1931 2,559,989Nyrop July 10, 1951 2,561,394 Marshall July 24, 1951 2,584,973 AndermattFeb. 12, 1952 FOREIGN PATENTS 695,266 Germany Aug. 21, 1940 530,613Great Britain Dec. 16, 1940 748,698 Germany Nov. 8, 1944 481,786 CanadaMar. 18, 1952

1. A METHOD OF TREATING A LIQUID MIXTURE CONTAINING SOLID MATTER DISSOLVED OR SUSPENDED THEREIN IN ORDER TO RECOVER THE SOLID MATTER IN DIVIDED FORM, VERY SOLUBLE IN A LIQUID, CONSISTING IN PROJECTING THIS LIQUID MIXTURE AT VERY HIGH SPEED WITH THE ASSISTANCE OF CENTRIFUGAL FORCE AND IN THE FORM OF A THIN HORIZONTAL SHEET IN THE UPPER PORTION OF A HOT-ATMOSPHERE DRYING TOWER, AND TO COLLECT THE POWDERED PRODUCT AT THE BOTTOM OF SAID TOWER, ACCORDING TO WHICH THE FINEST PARTICLES OF THE POWDERED PRODUCT ARE EXTRACTED BY SUCTION IN SAID TOWER BELOW THE HORIZONTAL SHEET OF LIQUID MIXTURE AND ARE PROJECTED AT VERY HIGH SPEED WITH THE ASSISTANCE OF CENTRIFUGAL FORCE AND IN THE FORM OF A THIN HORIZONTAL SHEET AT A LEVEL HIGHER THAN THAT OF SAID SHEET OF LIQUID MIXTURE AND A GAS IS BLOWN THROUGH THESE SHEETS IN ORDER TO BLOW THE SHEET OF THE FINEST PARTICLES OF THE POWDERED PRODUCT AGAINST THE SHEET OF LIQUID MIXTURE. 